US4084595A - Transcutaneous nerve stimulator - Google Patents

Abstract

Transcutaneous nerve stimulating apparatus wherein a portable, battery-operated variable pulse width, variable pulse rate oscillator is coupled through a variable amplitude current amplifying device to a set of electrodes adapted to be positioned upon the skin of a patient in proximity to a pain exhibiting area. The electrical signals or impulses are transmitted through the skin to the underlying nerves and serve to block the pain.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to electromedical therapeutic apparatus and more specifically to an improved transcutaneous nerve stimulating apparatus for alleviating pain through the selective application of variable amplitude, variable pulse rate, variable pulse width electrical pulses to the skin in the area in which pain is experienced. It has been found that a proper application of such pulses serves to block the nerve responses and produce a beneficial effect.

In accordance with the teachings of the present invention, an integrated circuit timing network, energized by a rechargeable direct current battery is connected to an external resistor/capacitor charging circuit to form an astable oscillator whose pulse width and pulse rate are manually adjustable. The oscillator is coupled through a transistor current switching network and a step-up transformer to first and second pairs of electrodes. A current balancing network coupled between the output of the transformer and the electrodes allows the transformer output to be apportioned between the first and second electrode pairs. Another network, including a light emitting diode, is coupled to the integrated circuit timing network and is arranged to blink on and off when the rechargeable battery potential falls below a prearranged value, thus signaling the need for recharging.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide an improved transcutaneous nerve stimulator which is portable, compact and convenient to operate.

Another object of this invention is to provide a portable transcutaneous nerve stimulator in which the amplitude, rate and pulse width of the applied electrical signals are selectively variable over a range of values by the patient.

Still another object of the invention is to provide an electronic pulse generator having a rechargable energy supply along with means for visually indicating the fact that the state of charge on the energy supply has deteriorated below a predetermined threshold value.

These and other objects and advantages of the invention will become apparent from a reading of the following detailed specification in conjunction with the accompanying drawings in which:

FIG. 1 is a pictorial drawing of the apparatus, showing the various controls; and

FIG. 2 is a schematic diagram of the circuitry used in the preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, there is shown a perspective pictorial view of the transcutaneous nerve stimulator package arrangement. The package includes a substantially rectangular casing 1 which may be molded or otherwise formed from a suitable material such as plastic. The size of the package may, for example, be one inch thick by 3, inches wide by five inches long.

Located at the front end as viewed in FIG. 1, is a step-like projection orextension 2 which is integrally formed with the rest of the case 1. A plurality of thumb-wheeltype control knobs 3, 4, 5 and 6 are mounted on shafts (not shown) which extend through apertures formed in thevertical riser 7. As will be explained more fully hereinbelow when the details of the electronic circuitry are described, these control knobs permit the user to control the rate, amplitude and pulse width of the electrical stimulating pulses produced by the transcutaneous nerve stimulator of this invention, as well as to control the balance of the electrical energy between first and second pairs of electrodes.

Affixed to the vertical front surface of theextension 2 is adisplay panel 8 having printed information thereon indicating the nature of the control obtained by the associated thumb-wheels 3, 4, 5 and 6. More specifically, thumb-wheel orknob 3 controls the balance of potential between first and second pairs of electrodes. Similarly, thumb-wheel 4 may be used to adjust the width of the stimulating pulses applied to the skin of the user via the electrodes (not shown). Thumb-wheels 5 and 6 respectively control the pulse rate and amplitude of the stimulating pulses. In addition, thumb-wheel 6 controls an "on-off" switch which is connected between the power for the unit and the electrical circuitry energized thereby.

First and second pairs of receptacles orjacks 9 and 10 are formed in thedisplay panel 8 and extend into the casing 1 where they connect to operative elements of the electrical circuitry housed within the casing. Also illustrated in FIG. 1, on the face of thedisplay panel 8 is anindicator 11 which, in the preferred embodiment, comprises a light-emitting diode (LED). As will be explained further, theindicator 11 serves to apprise the user of the charge condition of the energy source used to power the transcutaneous nerve stimulator of this invention.

The power source for the present invention is preferably a rechargeable DC battery pack (not shown). This pack is designed to be inserted and removed from its operative location within the housing 1 through an opening (not shown) formed in therear end 12 of the housing. Because of its size and weight (approximately nine ounces) it can be seen that the device is readily portable and conveniently can be carried in a shirt pocket or, if desired, secured by a belt to a desired location on the body of the user.

Now that the general physical features of the device have been described, consideration will now be given to the electrical circuitry used in implementing the preferred embodiment.

Referring to FIG. 2, there is shown a DCrechargeable battery 13 which is connected between theB+ bus 14 and aground bus 15. Thebattery 13 may be such as to produce a potential difference of approximately five volts across its terminals when fully charged, but limitation to such a value is not intended. The B+bus 14 is connected by aconductor 16 to the V_cc bus 17.

Connected between the V_cc bus 17 and theground bus 15 is an integratedcircuit chip 18. In the preferred embodiment of this invention, thechip 18 may be aType 556 dual timer device such as manufactured by the Fairchild Semiconductor Division of the Fairchild Camera and Instrument Corporation. Thechip 18 has 14 input/output pins which are respectively identified by the small numerals 1 through 14 located adjacent to the rectangular block representing theType 556 chip. One desiring additional information concerning the construction and mode of operation of this integrated circuit chip is referred to the application notes provided by the manufacturers. For example, reference is made to the handbook entitled "Fairchild Linear Integrated Circuits" copyrighted in 1976 Lk and published by the Fairchild Camera and Instrument Company.

Pin 1 of thechip 18 is connected to ajunction 19 between aresistor 20 and a semiconductor diode 21. The other terminal ofresistor 20 is connected to ajunction point 22 between the series combination of aresistor 23 and aresistor 24.Resistors 23 and 24 are serially connected with a capacitor 25 between theVcc bus 17 and theground bus 15.Pin 2 andPin 6 of thechip 18 are connected together and to thejunction point 26 formed between theresistor 24 and the capacitor 25.Pin 3 ofIC chip 18 is coupled by means of a capacitor 27 to theground bus 15.Pin 4 ofchip 18 is connected by aconductor 28 to the V_cc bus 17.Pin 5 ofchip 18 is connected through a series combination of a resistor 29 and a semiconductor diode 30 to ajunction point 31 to which the cathode of the diode 21 is connected. Connected betweenjunction 31 and theground bus 15 is a light-emittingdiode 32.Pin 7 ofchip 18 is connected directly to theground bus 15 by aconductor 33.

Pin 8 andPin 12 of thechip 18 are connected together by ajumper 34 at thejunction point 35 which, in turn, is connected by aconductor 36 to ajunction 37 formed between acapacitor 38 and a series combination ofresistor 39 and apotentiometer 40. The end ofpotentiometer 40, not common toresistor 39, is connected to theVcc bus 17. Coupled between the V_cc bus 17 andPin 9 ofchip 18 is a series combination of first andsecond resistors 41 and 42 and apotentiometer 43.Pin 10 andPin 14 ofchip 18 are connected together and to the V_cc bus 17 by way of aconductor 44.Pin 13 ofchip 18 is coupled through aseries resistor 45 and a parallel combination of aresistor 46 and apotentiometer 47 to aconductor 48 which is connected to thejunction point 37.

Acapacitor 49 is connected directly in parallel with thevoltage source 13 between theB+ bus 14 and theground bus 15. Thewiper arm 50 of thepotentiometer 43 is connected in common with the base electrodes of a plurality of transistors includingPNP transistors 51, 52 and 53. The emitter electrodes of each of these transistors are tied directly to theB+ bus 14 and the collector electrodes thereof are connected in common to ajunction point 54.

Theprimary winding 55 of a step-up transformer 56 is connected between thejunction 54 and theground bus 15. The step-up transformer 56 has asecondary winding 57 and connected in parallel with this secondary winding is acapacitor 58. Theupper terminal 59 ofsecondary winding 57 is connected to thewiper arm 60 of a balancing potentiometer 61. Opposite ends of the potentiometer 61 are connected to thejack terminals 9 and 10 (FIG. 1).

This completes a description of the various electrical connections and components used in the implementation of the transcutaneous nerve stimulator of the present invention. Consideration will next be given to the mode of operation of this circuit.

Operation -- FIG. 2

Before one can understand the operation of the overall circuit of FIG. 2, it is necessary to have some knowledge of the construction and mode of operation of theType 556integrated circuit chip 18 used therein. As is fully described in the aforereferences Fairchild Linear Integrated Circuit 1976 Handbook, theType 556 IC chip is a dual timing circuit. More specifically, contained within thechip 18 are two identical timer units. In the figure, Pins 1 through 7 provide the input, output and control connections to the first of the two timer circuits contained withinchip 18, whilePins 8 through 14 provide the input, output and control functions for the second of the two timer units. In the preferred embodiment, the first of the two timer units is used to provide a visual indication that the battery has discharged to a point where recharging thereof is in order. More specifically, the first timer unit is connected so as to operate as an astable multivibrator whose output atPin 5 is coupled through a resistor 29 and the diode 30 to the anode electrode ofLED 32. As the multivibrator output oscillates between a predetermined positive voltage and ground, thejunction 31 is alternately clamped at ground and allowed to assume a relatively high potential to thereby cause theLED 32 to turn on and off at a rate determined by the parameters ofresistors 23, 24 and capacitor 25. In order for the timer unit to operate in an astable mode, the "reset"Pin 4 is tied to a high potential by way ofconductor 28 andPin 2 andPin 6 are connected together and to thejunction point 26 between the capacitor 25 and theresistor 24. It is this jumper connection betweenPins 2 and 6 which causes the timer unit to trigger itself, i.e., free run as a multivibrator. When operating in the astable mode, the capacitor 25 charges and discharges between 1/3 V_cc and 2/3 V_cc. The charging and discharging times of the capacitor 25 are independent of the magnitude of the supply voltage and therefore the frequency of oscillation is also substantially independent of supply voltage.

The point at which theLED 32 begins to blink can be expressed by the following inequality: ##EQU1## In the foregoing expression: V_D32 is the voltage drop across the LED;

V_d21 is the drop across diode 21;

R20 and R23 and R25 are expressed in ohms; and

V_b is the battery potential.

Thus, one can see that by judiciously selecting the values of theresistors 20 and 23, it is possible to predetermine the point at which the visual indication of a low battery potential will take place.

The second of the two timer units contained on theIC chip 18 along with the circuitry shown to the right of thechip 18 in FIG. 2 provides the nerve stimulating output pulses and the means for adjusting the amplitude, duration, frequency and balance thereof. Again, the connection between thetrigger Pin 8 and thethreshold Pin 12 of the chip 18 (conductor 34) causes the second timer unit onchip 18 to also operate in an astable mode. To prevent false resetting of the astable multivibrator, thereset Pin 10 ofchip 18 is connected by means ofconductor 44 to a relatively high potential. The output from the astable multivibrator appears atPin 9. Thepotentiometer 40 in series with theresistor 39 controls the charging time of thecapacitor 38. These three components determine the frequency at which output pulses will be produced. In the preferred embodiment,potentiometer 40,resistor 39 andcapacitor 38 are of such a value that the frequency of the output signals can be made to vary between 10 and 100 Hz. Theresistors 45 and 46 along with thepotentiometer 47 in parallel withresistor 46, control the discharge time of thecapacitor 38 and therefore by appropriately positioning the wiper arm of thepotentiometer 47, the pulse width of the output from the timer unit can be controlled. In the preferred embodiment, the component values are chosen such that the pulse duration can be made to vary between 10 and 500 microseconds. For a given value of resistance in thepotentiometer 47, the values ofresistors 45 and 46 are chosen to give the desired end points for permissible pulse width.

As previously mentioned, the output signals from the second timer unit on thechip 18 appear atPin 9 and swing between ground and a positive value determined by the ohmic values ofresistors 40, 41 and 42 and thepotentiometer 43. The output signals are used to control the conduction state of the parallelconnected transistors 51, 52 and 53. The conduction level in these three transistors, in turn, may be controlled by the setting of thewiper arm 50 on thepotentiometer 43. Hence, it is possible to control the amount of current flowing from thepositive bus 14, through the parallel paths afforded bytransistors 51, 52 and 53 and through the primary winding 55 of the step-uptransformer 56. Thus, the setting of thewiper arm 50 determines the amplitude of the output pulses used to stimulate the body. The amplitude can be made to vary between 0 V and 35 V. In order to prevent thermal run-away in the parallelconnected transistors 51, 52 and 53, it may be desirable to include resistors of identical ohmic values in series with the emitters of these transistors.

The changing current caused by the application of the timer output pulses to theparallel transistors 51, 52 and 53 causes a voltage to be induced across the secondary winding 57 of thetransformer 56. Thecapacitor 58 connected in parallel with the secondary winding 57 serves to protect thetransistors 51, 52 and 53 when an open circuit exists between the electrode jacks 9 and 10. The potentiometer 61 provides a means for balancing the distribution of load current as between the electrodes connected tojacks 10 and the electrodes connected to thejacks 9.

Thus, there is provided by this invention apparatus for producing variable amplitude, variable pulse width, variable frequency output signals to first and second electrode pairs. In addition, the invention includes circuitry for indicating when the level of charge on the rechargeable power pack has dropped below a given threshold.

Accordingly, it is seen that the present invention fully accomplishes its intended objects. While there has been disclosed and described in detail a preferred embodiment of the invention, that has been done by way of illustration, and not by way of limitation. It is realized that the transcutaneous nerve stimulator of the present invention can assume additional forms, and it is intended to include within the scope of the appended claims all modifications and variations naturally occurring to those skilled in the art.

Claims (7)

I claim:

1. A transcutaneous nerve stimulator comprising in combination:

(a) an astable multivibrator having a first resistance/capacitance timing circuit for controlling the frequency of the output pulses produced by said astable multivibrator and a second resistance/capacitance timing circuit for controlling the pulse width of said output pulses;

(b) semiconductor current control means coupled by variable impedance means to receive said output pulses from said multivibrator;

(c) a source of direct current voltage connected to said multivibrator, said first and second resistance/capacitance circuits and to said semiconductor current control means;

(d) a transformer having a primary winding connected in series with said semiconductor current control means, the series combination being connected across said source of direct current voltage, and a secondary winding;

(e) means coupling said secondary winding to first and second pairs of output terminals to which stimulator electrodes may be connected;

(f) a third resistance/capacitance timing circuit connected across said source of direct current voltage;

(g) a voltage divider connected to said source of direct current voltage for sensing the magnitude thereof;

(h) indicating means connected to said voltage divider; and

(i) a second astable multivibrator energized by said source of direct current voltage having an output terminal coupled to said indicating means and a trigger terminal connected to said third resistance/capacitance timing network, whereby said indicating means is continously energized when the magnitude of said direct current voltage is above a predetermined level and is alternately energized and deenergized when the magnitude of said direct current voltage drops said predetermined level, at a rate determined by said third resistance/capacitance timing circuit.

2. Apparatus as in claim 1 wherein the resistance in said first and second resistance/capacitor timing circuits is variable such that the frequency and pulse width of said output pulses produced by said multivibrator are manually adjustable.

3. Apparatus as in claim 1 wherein said variable impedance the means coupling the output pulses from said mutivibrator to said semiconductor current control means comprises a potentiometer for allowing manual control of the amplitude of the voltage induced across said secondary winding of said transformer.

4. Apparatus as in claim 3 wherein said means coupling said secondary winding to said first and second pairs of output terminals is a potentiometer having opposite ends thereof connected individually to a first output terminal of said first and second pairs of output terminals and its positionable tap connected to one end of said second winding, and wherein the second output terminal of said first and second pairs of output terminals are connected in common to the other end of said secondary winding such that the amount of current flowing to said first output terminals of said first and second pairs of output terminals can be balanced.

5. Apparatus as in claim 1 wherein said indicating means is a light-emitting diode.

6. Apparatus as in claim 1 wherein said astable multivibrators are semiconductor integrated circuits.

7. Apparatus as in claim 1 wherein said source of direct current voltage is a nickel-cadmium rechargeable battery.

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